1. Mesozoic Geology

2. Introduction The Mesozoic began 248 mya and ended 65 mya
Three periods - Triassic, Jurassic, Cretaceous
breakup of Pangaea was the major geologic event
tectonism and sedimentation are used to classify the Mesozoic in N. America
Note the overlap in three styles of Cordilleran Orogeny

3. Tectonism and Sedimentation
Seaway drains

4. 1. The Breakup of Pangaea
The movement of continents during and after the breakup affected global climates
Sea-level changes due MOR heating and growth, then cooling

5. Pangaea - Early Triassic
Pangaea ran from pole to pole and
straddled the equator.
The Panthalassa Ocean allowed equatorial waters to warm polar lands.
The East coast indent is called the
“Tethys Sea”
Tethys
Panthalassa
Panthalassa

6. Late Triassic – Rifting E Orogeny W
We will consider mostly North America for this lecture
Orogeny
Rift
Better look at Tethys

7. Pangaea – Early Jurassic

8. E Jurassic – Atlantic Rift Shallow
Note offshore Terranes

9. E Jurassic – Another Look
Orogeny
New Sea
Wrangellia

10. Pangaea: mid-Jurassic

11. Latest Jurassic – Early Cretaceous
Atlantic Connected with Tethys
Africa rotation closes Tethys

12. Tethys
Atlantic

13. Late K – Epeiric Sea until 70 mya

14. Mesozoic Global Climates
Carbonates (for example the stable isotope ratio d13C) reveal large concentrations of carbon dioxide present in the Mesozoic atmosphere.
This suggests a greenhouse climate.
No glaciers, no coal, so CO2 abundant.
Greenhouse gasses pass sunlight which hits the land and sea. Re-radiate heat (IR)
Greenhouse gasses hold the heat, not lost to space as quickly. Warmer equilibrium.

15. Global Climates in the Mesozoic
Mesozoic climates were more equable than today, lacked the strong north-south climate zones.
Mesozoic plant fossils indicate subtropical conditions in high latitude locations
Seasonal differences were monsoonal
Cycads

16. Next: Mesozoic Tectonics NA
Cretaceous : global rise in sea level until mya, vast MOR
Jurassic:
Atlantic opens E,
began building the Cordillera W,
Gulf of Mexico begins to form and experiences evaporite deposition
Late Triassic: Begin rifting in East
Start here

18. Late Triassic: Rifting opens the Atlantic
The Newark Supergroup documents the rifting of Pangaea to form the Atlantic
Early Triassic saw coarse detrital sediments deposited from the erosion of Appalachian highlands
fault-block basins developed as N. America separated from Africa and filled with nonmarine sediment plus dikes and sills
eroded to a flat plain by the Cretaceous

19. Mesozoic rift basins
Kean University

20. Structure of the Newark basin
Note how faulting offsets sedimentation

21. Lake cycles, East Berlin formation
Alternating wet and dry climate
due 21000y Milankovitch cycle of tilt axis wobble
Also 100,000 year cycles due to orbit eccentricity

22. E. Jurassic Gulf Coast Evaporites
200 mya is just outside our door
Restricted Basin
Lots of evaporation

23. Gulf Coastal Region
First, as continents separate, restricted basin, thick evaporites formed in the Gulf
Normal marine deposition returned to the Gulf by Late Jurassic, with transgressions and regressions
thousand of meters of sediments were deposited
Does this cross-section show
a transgression or regression?

24. Gulf Coast continental margin
Rising Salt Domes tilt sediments
Concentrate petroleum

25. Discussion: Petroleum exploration around salt domes
Squint: The Petroleum is in the bright spots, at the boundary of the salt and pushed up sediment. Tells us where to look, saves money, lowers cost of fuel.

26. Next: Western North America Tectonics
Building the western margin of North America and the Cordillera

27. Displaced terranes – Western Cordillera
These terranes overlap in age but have different rock types, paleolatitudes and fossils. However, we can deduce when they accreted from this map.
Exercise: Arrange the following terranes by oldest to youngest time of accretion onto the west coast: Alexander, Cache Creek, Chugach, Eastern, Stikine, Taku, Tracy Arm, Wrangellia, Yukon-Takana

28. Western Region Cordilleran Orogeny
Laramide – Vertical blocks-built the present day Rockies K-Tertiary
Sevier – J-K thrust faulting to the east
Nevadan - Jurassic batholith intrusion in the Sierra Nevada and elsewhere on the western edge

29. Western Margin during Orogens
North America drifting west due opening of Atlantic
Westward subduction zones stopped when continental
crust arrived.
Late Triassic on, eastward
subduction of Farallon oceanic
crust continues Cordilleran Orogeny
Late J Early K Nevadan Batholiths
Remember the late Permian Sonoma?
It continued into the Early Triassic
Sonomia docking Late Pm –Early Triassic
Nevadan Orogeny east subduction Farallon

30. Sierra Nevada Mountains
Nevadan Orogeny:
Subduction formed batholith cores of continental volcanic arc once as tall as Andes

31. Mesozoic orogenic events
Thin-skinned tectonics
Cretaceous Sevier Wrangellia docking?
Later moved by transform fault?
K-T Laramide Continental Overide
Bouyant Subduction

32. Buoyant Subduction Laramide Orogeny
Vertical block uplift
Normal, thin-skinned
Now we understand weird looking Tetons
Approaching Continent pushes
accretionary wedge sediments
into forearc sediments

33. Sevier thin-skinned deformation
Using the layer colored sky blue, look at the faults.
Is the hanging wall mostly up or down? What kind of faults
are these?

34. Sevier thrust belt Precambrian and/or Paleozoic Sediments
thrust over younger Mesozoic rocks

35. let’s look down here

36. Look in detail at western plate margin
This area has much simpler geology
Franciscan Range, Great Valley Group, and Sierra Nevada Volcanics and Plutonics

37. Next: Mesozoic Sedimentation on the Craton
Cretaceous
extensive marine deposition until 70mya, thins to the east
Jurassic
clean cross-bedded sandstones
marine sediments in the Sundance Sea
Triassic
shallow-water marine clastics
red beds
Foreland Basin!

38. North America - Triassic
Marine deposition limited to western margin
Volcanic Arc sends frequent ashfalls eastward
Newark
Pollen
similar
Chinle
Note Equator

39. Late Triassic Chinle Fm.
Mudstones and Sandstones of stream deposits, volcanic ash,
with fossil trees (the Petrified Forest!)
Texas, New Mexico, northern Arizona, Nevada, Utah, and western Colorado
Pollen studies show that the Chinle is the same age as early Newark Supergroup

40. Triassic caliche paleosol- Nova Sc.
Source of carbonates for d13C measurements. Results suggest high CO2 in atmosphere
Similar in Newark Supergroup

41. North America - Jurassic period
Dry region
in the rain shadow of the beginning Nevadans
Zuni Transgression

42. Sedimentation
Seaway drains
Evaporites

43. Jurassic Eolian sandstone
Navaho SS, S. Utah

44. Jurassic Morrison Formation
Jurassic Morrison Formation
Paul Olsen's Dinosaur Course
Stream Deposits, huge sauropods Apatosaurus, also Stegosaurus, carnivore Allosaurus

45. Fossils of Jurassic dinosaurs
Morrison Formation sandstones, DNM, Vernal, Utah

46. Giant sauropod and Allosaurus bones,
Mossison Fm., DNM, Vernal Utah

47. Late Cretaceous really big epeiric sea
Dinosaurs on the North Slope
Until 70 mya
Land
Land

49. Western Interior Seaway Regression
Did the Sevier Orogenic Belt form before or after the Navaho SS, lower left?
Did the Sevier Orogenic Belt form before or after the Fox Hills SS, upper right?
Fox Hills SS
Western Interior Seaway Regression
Western Interior Seaway Transgression
Navaho SS
Dakota SS is bottom right

50. Dakota Sandstone
Early Cretaceous shallow sea sediments gently folded by Sevier Orogeny.

51. Then, at my, Regression

52. Western Interior Seaway Regression
In Montana the sequence is similar. Above the marine Pierre Shale (ammonites) and Claggett Sandstone (nearshore and beach) is the Late Cretaceous Judith River Fm. containing dinosaur bones and conifers in stream deposits. Is this sequence a transgression or a regression?
Western Interior Seaway Regression
Pierre
Shale
Western Interior Seaway Transgression

53. 75 mya Regression
Mesa Verde Sandstones over Mancos Shale: Coarsening Upward

54. K-T Boundary

55. End of Mesozoic Geology